Plastic materials are widely used as support for carrying a functional layer such as an image recording layer, an electro-conductive layer, a light modulating layer, an adhesive layer, etc. Many applications require the use of a dimensionally stable support for carrying such a functional layer. Known examples thereof are graphic-arts applications and photomasks for the manufacture of printed circuit boards. In these applications glass plates are often used as a support because glass is characterised by excellent dimensional stability in varying conditions of temperature or humidity, contrary to a plastic support.
Another example of an application which requires high thermal and dimensional stability is the manufacturing of flat panel displays such as liquid crystal displays (LCDs), wherein glass plates are used as support for carrying a plurality of functional layers such as colour filters, electroconductive layers and liquid crystal orientation layers. Glass plates used in flat panel displays such as LCDs have a typical thickness in the range from 0.7 to 1.1 mm. At least two such glass plates are needed in each display and the weight of a display is mainly determined by the size and thickness of these glass plates. In "Fourth-Generation LCDs--EIAJ Display Forecast", published in "Display Devices", Spring '96, Serial no. 13, p.14-19 (published by Dempa Publications Inc., Tokyo), it is emphasised that weight reduction of flat panel displays is an important need in the art, especially when such displays are to be incorporated in mobile applications such as portable computers. A further reduction of the thickness of the glass plates is however limited due to the high brittleness of such thin glass.
In addition to a high thermal and dimensional stability, glass has many other beneficial properties compared to plastic materials, e.g. the ease of recycling, excellent hardness and scratch resistance, high transparency, good resistance to chemicals such as organic solvents or reactive agents, low permeability of moisture and gases, and a very high glass transition temperature, enabling the use of high-temperature processes for applying a functional layer. However, the main problems associated with the use of glass as support for applying a functional layer are the low flexibility, the high specific weight and the high risk of glass breakage, especially when thin glass is used. Due to the low flexibility of glass, the coating of a functional layer on glass is typically carried out in a batch process (sheet by sheet), whereas the coating of a plastic support is generally performed as a continuous process, e.g. using a web or roll coater. It is self-evident that the productivity and cost efficiency of a continuous (web) coating process is significantly higher than of a batch (sheet) coating process.
EP-A 716 339 describes a process using a flexible glass web, which can be wound up around a core so as to obtain a roll of glass. Said glass can be unrolled and coated with a functional layer in a continuous web coating method. Said flexible glass is characterised by (i) a thickness lower than 1.2 mm, (ii) a failure stress (under tensile stress) equal to or higher than 1.times.10.sup.7 Pa and (iii) an elasticity modulus (Young's modulus) equal to or lower than 1.times.10.sup.11 Pa. Glass according to these specifications is indeed flexible and can be wound around a core. However, the probability of web breakage is high because a sharp local pressure applied on the surface of the glass web is sufficient to break the glass. Even the smallest probability of web breakage during coating is to be eliminated when carried out on an industrial scale, since the advantages associated with a continuous web coating process are then lost due to the interruption of the process.
The above problem is also recognised in WO 87/06626, wherein it is stated that thin glass having a thickness of 1 to 15 mils breaks almost immediately when rolled up. As a solution to protect a glass web which is wound around a core, WO 87/06626 describes the use of an interleave which prevents glass-to-glass contact. Said interleave is a non-abrasive material such as an embossed polyester film. However, when the glass web is unwound from its core, the interleave is separated from the glass and from then on, the same problems arise as discussed above with regard to EP-A 716 339.
In order to combine the advantageous properties of different materials it is known to adhere sheets of said different materials to each other so as to obtain a laminate. A well known example is security glass used in car windshields as described in FR 2.138.021 and EP-A 669 205. The latter patent application describes a glass/plastic laminate comprising a glass pane, an intermediate adhesive layer and a plastic pane, wherein the glass has a thickness from 30 to 1000 .mu.m. The glass is preferably a chemically hardened glass and before lamination, a functional layer can be applied to the glass. After lamination, said functional layer is sandwiched between the glass and the plastic layer and is thereby protected from outside influences. A laminate of a thin chemically hardened glass and a plastic support has also been described in U.S. Pat. No. 3,471,356. However, thin chemically hardened glass is not sufficiently strong to reduce the risk of glass breakage adequately.